/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package compressionFilters;

import java.io.IOException;
import java.io.OutputStream;
import java.util.zip.GZIPOutputStream;

import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;

/**
 * Implementation of <b>ServletOutputStream</b> that works with the
 * CompressionServletResponseWrapper implementation.
 * 
 * @author Amy Roh
 * @author Dmitri Valdin
 * @version $Revision: 500668 $, $Date: 2007-01-28 07:07:51 +0800 (星期日, 28 一月
 *          2007) $
 */

public class CompressionResponseStream extends ServletOutputStream {

	// ----------------------------------------------------------- Constructors

	/**
	 * Construct a servlet output stream associated with the specified Response.
	 * 
	 * @param response
	 *            The associated response
	 */
	public CompressionResponseStream(HttpServletResponse response)
			throws IOException {

		super();
		closed = false;
		this.response = response;
		this.output = response.getOutputStream();

	}

	// ----------------------------------------------------- Instance Variables

	/**
	 * The threshold number which decides to compress or not. Users can
	 * configure in web.xml to set it to fit their needs.
	 */
	protected int compressionThreshold = 0;

	/**
	 * Debug level
	 */
	private int debug = 0;

	/**
	 * The buffer through which all of our output bytes are passed.
	 */
	protected byte[] buffer = null;

	/**
	 * The number of data bytes currently in the buffer.
	 */
	protected int bufferCount = 0;

	/**
	 * The underlying gzip output stream to which we should write data.
	 */
	protected OutputStream gzipstream = null;

	/**
	 * Has this stream been closed?
	 */
	protected boolean closed = false;

	/**
	 * The content length past which we will not write, or -1 if there is no
	 * defined content length.
	 */
	protected int length = -1;

	/**
	 * The response with which this servlet output stream is associated.
	 */
	protected HttpServletResponse response = null;

	/**
	 * The underlying servket output stream to which we should write data.
	 */
	protected ServletOutputStream output = null;

	// --------------------------------------------------------- Public Methods

	/**
	 * Set debug level
	 */
	public void setDebugLevel(int debug) {
		this.debug = debug;
	}

	/**
	 * Set the compressionThreshold number and create buffer for this size
	 */
	protected void setBuffer(int threshold) {
		compressionThreshold = threshold;
		buffer = new byte[compressionThreshold];
		if (debug > 1) {
			System.out.println("buffer is set to " + compressionThreshold);
		}
	}

	/**
	 * Close this output stream, causing any buffered data to be flushed and any
	 * further output data to throw an IOException.
	 */
	public void close() throws IOException {

		if (debug > 1) {
			System.out.println("close() @ CompressionResponseStream");
		}
		if (closed)
			throw new IOException("This output stream has already been closed");

		if (gzipstream != null) {
			flushToGZip();
			gzipstream.close();
			gzipstream = null;
		} else {
			if (bufferCount > 0) {
				if (debug > 2) {
					System.out.print("output.write(");
					System.out.write(buffer, 0, bufferCount);
					System.out.println(")");
				}
				output.write(buffer, 0, bufferCount);
				bufferCount = 0;
			}
		}

		output.close();
		closed = true;

	}

	/**
	 * Flush any buffered data for this output stream, which also causes the
	 * response to be committed.
	 */
	public void flush() throws IOException {

		if (debug > 1) {
			System.out.println("flush() @ CompressionResponseStream");
		}
		if (closed) {
			throw new IOException("Cannot flush a closed output stream");
		}

		if (gzipstream != null) {
			gzipstream.flush();
		}

	}

	public void flushToGZip() throws IOException {

		if (debug > 1) {
			System.out.println("flushToGZip() @ CompressionResponseStream");
		}
		if (bufferCount > 0) {
			if (debug > 1) {
				System.out.println("flushing out to GZipStream, bufferCount = "
						+ bufferCount);
			}
			writeToGZip(buffer, 0, bufferCount);
			bufferCount = 0;
		}

	}

	/**
	 * Write the specified byte to our output stream.
	 * 
	 * @param b
	 *            The byte to be written
	 * 
	 * @exception IOException
	 *                if an input/output error occurs
	 */
	public void write(int b) throws IOException {

		if (debug > 1) {
			System.out.println("write " + b + " in CompressionResponseStream ");
		}
		if (closed)
			throw new IOException("Cannot write to a closed output stream");

		if (bufferCount >= buffer.length) {
			flushToGZip();
		}

		buffer[bufferCount++] = (byte) b;

	}

	/**
	 * Write <code>b.length</code> bytes from the specified byte array to our
	 * output stream.
	 * 
	 * @param b
	 *            The byte array to be written
	 * 
	 * @exception IOException
	 *                if an input/output error occurs
	 */
	public void write(byte b[]) throws IOException {

		write(b, 0, b.length);

	}

	/**
	 * Write <code>len</code> bytes from the specified byte array, starting at
	 * the specified offset, to our output stream.
	 * 
	 * @param b
	 *            The byte array containing the bytes to be written
	 * @param off
	 *            Zero-relative starting offset of the bytes to be written
	 * @param len
	 *            The number of bytes to be written
	 * 
	 * @exception IOException
	 *                if an input/output error occurs
	 */
	public void write(byte b[], int off, int len) throws IOException {

		if (debug > 1) {
			System.out.println("write, bufferCount = " + bufferCount
					+ " len = " + len + " off = " + off);
		}
		if (debug > 2) {
			System.out.print("write(");
			System.out.write(b, off, len);
			System.out.println(")");
		}

		if (closed)
			throw new IOException("Cannot write to a closed output stream");

		if (len == 0)
			return;

		// Can we write into buffer ?
		if (len <= (buffer.length - bufferCount)) {
			System.arraycopy(b, off, buffer, bufferCount, len);
			bufferCount += len;
			return;
		}

		// There is not enough space in buffer. Flush it ...
		flushToGZip();

		// ... and try again. Note, that bufferCount = 0 here !
		if (len <= (buffer.length - bufferCount)) {
			System.arraycopy(b, off, buffer, bufferCount, len);
			bufferCount += len;
			return;
		}

		// write direct to gzip
		writeToGZip(b, off, len);
	}

	public void writeToGZip(byte b[], int off, int len) throws IOException {

		if (debug > 1) {
			System.out.println("writeToGZip, len = " + len);
		}
		if (debug > 2) {
			System.out.print("writeToGZip(");
			System.out.write(b, off, len);
			System.out.println(")");
		}
		if (gzipstream == null) {
			if (debug > 1) {
				System.out.println("new GZIPOutputStream");
			}
			if (response.isCommitted()) {
				if (debug > 1)
					System.out
							.print("Response already committed. Using original output stream");
				gzipstream = output;
			} else {
				response.addHeader("Content-Encoding", "gzip");
				gzipstream = new GZIPOutputStream(output);
			}
		}
		gzipstream.write(b, off, len);

	}

	// -------------------------------------------------------- Package Methods

	/**
	 * Has this response stream been closed?
	 */
	public boolean closed() {

		return (this.closed);

	}

}
